1. Field of the Invention
The present invention generally relates to an improved mounting enclosure and mounting arrangement for apparatus used in metal melting, refining and processing, for example, steel making in an electric arc furnace (EAF), and more particularly, to a mounting arrangement for an auxiliary burner or lance relatively close to a molten metal bath to increase its efficiency.
2. Description of Background Art
An electric arc furnace makes steel by using an electric arc to melt one or more charges of scrap metal which is placed within the furnace. The scrap is charged by dumping it into the furnace through the roof from buckets which also may include charged carbon and slag forming materials. The arc melts the scrap into a molten pool of metal, called an iron carbon melt, which accumulates at the bottom or hearth of the furnace. After a flat bath has been formed by melting of all the scrap introduced, the electric arc furnace enters a refining or decarburizing phase. In this phase, the metal continues to be heated by the arc until the slag forming materials combine with impurities in the iron carbon melt and rise to the surface as slag. When the iron carbon melt reaches a boiling temperature, the charged carbon in the melt combines with any oxygen present in the bath to form carbon monoxide bubbles which rise to the surface of the bath. Generally, at this time supersonic flows of oxygen are blown at the bath with either lances or burners to produce a decarburization of the bath by the oxidation of the carbon contained in the bath. By simultaneously boiling the bath and injecting it with oxygen, the carbon content of the bath is reduced to under 2% carbon whereby the iron carbon melt becomes steel. The carbon in the steel bath is thereafter further reduced until the grade of steel desired is produced, down to less than 0.2% for low carbon steels.
To assist in the steel making process, auxiliary burners or lances can be used for the addition of thermal energy by the combustion of fuel, the injection of oxidizing gas for melt refining, foamy slag production or post combustion of carbon monoxide, and the injection of particulates for slag and foamy slag production. In many instances, the oxidizing gas is introduced as a high velocity stream that may exceed sonic velocities. Laval nozzles, or other supersonic nozzle types, are usually used in the production of high velocity streams of oxidizing gas for injection into a steel making furnace. These supersonic gas flows are produced by the converging/diverging shape of the nozzle which at above a critical pressure causes the gas flow though the nozzle to become supersonic. It is also highly desirable to provide a subsonic flow of oxidizing gas for the burning of fuel, including regular fuel and carbon monoxide for post combustion, for the addition of auxiliary thermal energy, and the supersonic oxygen flow for providing oxygen in iron melt decarburization, assisting in foamy slag production or post combustion of carbon monoxide.
An auxiliary oxy/fuel burner which is useful in the process of steel production in electric arc furnaces and which provides subsonic and supersonic flows of oxygen through the same centrally located conduit is shown to advantage in a technical publication entitled xe2x80x9cAdvanced Burner Designxe2x80x9d by V. Shver, T. Pulliam, and M. Cohen (Shver, et al. I) dated November 1997. This burner is manufactured and commercially sold by Process Technology International, Inc. of Tucker, Ga., the assignee of the present invention. The subsonic flow is produced by providing a pressure in the supply conduit lower than the critical pressure of the supersonic nozzle being used in the conduit. When supersonic oxygen is needed, the pressure in the supply conduit is increased to above the critical pressure. The disclosure of Shver, et al. I is hereby incorporated by reference.
Another burner with the capability to introduce supersonic or subsonic oxidizing gas into an electric arc furnace is illustrated in U.S. Ser. No. 09/251,193, entitled xe2x80x9cMethod and Apparatus for Improved EAF Steelmakingxe2x80x9d, filed Feb. 16, 1999 in the name of V. Shver, and assigned commonly with the present application. Shver discloses an annular nozzle for producing a supersonic oxygen flow surrounding a carbon injection conduit forming a portion of a nozzle in a fluid cooled combustion chamber of the burner. The disclosure of Shver is hereby incorporated by reference.
Still another burner with the capability to introduce supersonic or subsonic oxidizing gas into an electric arc furnace is illustrated in U.S. Ser. No. 09/459,303, entitled xe2x80x9cImproved Method and Apparatus For Metal Melting, Refining and Processingxe2x80x9d, filed Dec. 10, 1999 in the names of V. Shver, et al. (Shver, et al. II), and assigned commonly with the present application. Shver, et al. II discloses a supersonic oxygen conduit in a side by side arrangement with a carbon injection conduit forming a portion of a nozzle in a fluid cooled combustion chamber of the burner. The disclosure of Shver, et al. II is hereby incorporated by reference.
Additionally, there are many other burners and lances which provide a supersonic oxidizing gas lancing capability and which provide for the introduction of other materials for use in an electric arc furnace.
The supersonic lancing mode is used in one instance for melt refining because the flow of oxygen must penetrate the molten metal in the hearth of the furnace. The increased velocity of the gas from accelerating it to a supersonic condition increases its momentum and thus depth of penetration into the melt. Another technique to increase the penetrating power of an oxidizing gas flow is to increase the flow rate by the use of a larger supersonic nozzle. While this advantageous to some extent, an excess of oxidizing gas is detrimental to the furnace components and the higher pressures needed for the larger nozzles rapidly become uneconomic.
The mounting of these burners and lances have generally been either through openings in the furnace which are used for other purposes, such as the slag door, roof holes or the EBT access panels, or in greater numbers through specially made openings in the water cooled panels of the side wall of the furnace. The specially made side wall openings allow the burners to be strategically mounted, for example, where there are cold spots in the furnace, or other desired places, possibly for the introduction of process materials. To improve the penetrating power and efficiency of the supersonic oxidizing gas flows from the burners, the mountings of the burners in the furnace side wall have been as far down on the side panels as possible. However, there has been a limit to the mounting of the burners in proximity to the melt because of the structure of many present day furnaces.
The hearth of the furnace is made of refractory materials to contain the molten metal during steel processing. The hearth of the furnace forms a step with the water cooled panels of the furnace side wall where they connect. In the past, the burners have been mounted high enough and at an suitable angle on the side walls where the introduced flows of super sonic oxygen or other materials will miss the edge of the step. Even for those instances where such flows miss the step, the is some deterioration of the refractory by the highly reactive oxidizing gas flowing closely past it. For apparatus providing supersonic oxidizing gas flow this means the mounting angle and flow rates are not only dictated by the steel making process requirements but also by the structure of the furnace.
Therefore, there is a need to mount burners and lances with supersonic oxidizing gas capability closer to the molten metal and directed more to the center of the furnace so they can be more efficient in operation.
There is also a need to mount these burners and lances at optimum angles, to operate them at optimum flow rates and at optimum distances from the melt.
The invention provides a mounting enclosure for a burner, lance or similar apparatus and an improved arrangement for mounting such apparatus used in metal melting, refining and processing, particularly steel making in an electric arc furnace.
In one preferred embodiment, the mounting enclosure is a fluid cooled free standing block having a mounting aperture for a burner which extends the discharge opening of the burner past the step of the furnace. The preferred implementation of the mounting enclosure includes a front face adapted for the inner part of the furnace, a back face adapted to meet the side wall, and a width approximately that of the step between the side wall and the hearth of the furnace. In this manner, the mounting enclosure can rest on the step and be added to or removed from the furnace without any substantial change to the structure of the furnace. The mounting enclosure is manufactured from a material which is strong enough to withstand the scrap charging and steel and slag splashing of the furnace while also exhibiting a relatively high thermal conductivity. Preferably, the material used for the enclosure is cast iron which is inexpensive and can be easily produced with conduits for fluid cooling and the burner mounting aperture.
In a second preferred embodiment, the mounting enclosure is a fluid cooled box having a mounting aperture for a burner which extends the discharge opening of the burner past the step of the furnace. The preferred implementation of the mounting enclosure includes a front wall with a face adapted for the inner part of the furnace and side walls adapted to meet the furnace side wall of the furnace with a width approximately that of the step between the furnace side wall and the furnace hearth. The mounting enclosure is manufactured from a material which is strong enough to withstand the scrap charging and steel and slag splashing of the furnace while also exhibiting a relatively high thermal conductivity. Preferably, the material used for the mounting enclosure is copper which can be easily produced with conduits for fluid cooling and the burner mounting aperture.
Another aspect of the invention provides the mounting enclosure with a recess in its front face. An fluid cooled insert panel is then installed into the recess to provide additional cooling capacity for the front face of the mounting enclosure. Because the front face of the mounting enclosure may receive the direct radiation from the arc of the furnace, the insert is made out of a material of a high thermal conductivity, which may be the same as the mounting enclosure or even a higher thermal conductivity, preferably copper.
According to another preferred embodiment of the invention, the mounting enclosure further includes a slanted porch between its front face and back face. The slant of the porch lessens the area of the front face directly in line with the radiation of the arc while providing an increased area for fluid cooling. Further, the slant of the porch allows scrap to slide down into the molten bath and away from the mounting enclosure. Optionally, slag retaining means, preferably in the form of cast channels or corrugations, are provided on the porch and the sides of the mounting enclosure to retain a covering of the splashed slag to form a protective barrier over the enclosure.
A first mounting arrangement includes utilizing the mounting enclosure to mount a burner, lance or similar apparatus in a furnace, preferably a burner, lance or similar apparatus with at least supersonic lancing capability and preferably in an electric arc furnace. The burner or lance is mounted by passing it through an aperture in a water cooled side panel aligned with the mounting aperture in the mounting enclosure. Because the mounting enclosure is approximately the width of the step, the discharge opening of the burner is moved by that distance closer to the center of the furnace. The flame discharge opening will now also extend past the inner edge of the sill so that the burner flow pattern is not such a problem to the hearth material and other furnace equipment mounted nearby.
Another mounting arrangement utilizes the walled mounting enclosure to mount a burner, lance or similar apparatus in a furnace. Preferably, the burner, lance or similar apparatus has at least supersonic lancing capability and the furnace is an electric arc furnace. The walled mounting enclosure is inserted through an opening in the side wall of the furnace such that its side walls seal the opening and its front face extends to the edge of the sill. The burner, lance, or similar apparatus is mounted by passing it through the open back of the walled mounting enclosure into the apparatus mounting aperture. Because the mounting enclosure is approximately the width of the step, the discharge opening of the apparatus for burner flame and oxidizing gas lancing is moved by that distance closer to the center of the furnace. The discharge opening of the apparatus will also extend past the edge of the sill so that the burner flow and oxidizing gas flow patterns are not such a problem to the hearth material and other furnace equipment mounted nearby.
Yet another mounting arrangement utilizes the walled mounting enclosure to mount a burner, lance or similar apparatus in combination with a particulate injector in a furnace. Preferably, the burner, lance or similar apparatus has at least supersonic lancing capability, the particulate injector is a carbon injector and the furnace is an electric arc furnace. The walled mounting enclosure is inserted through an opening in the side wall of the furnace such that its side walls seal the opening and its front face extends to the edge of the sill. The burner, lance, or similar apparatus is mounted by passing it through the open back of the walled mounting enclosure into the apparatus mounting aperture. The particulate injector is mounted by passing it through the open back of the walled mounting enclosure into the particulate mounting aperture. Because the mounting enclosure is approximately the width of the step, the discharge opening of the apparatus for burner flame and oxidizing gas lancing is moved by that distance closer to the center of the furnace. The discharge opening of the apparatus will also extend past the edge of the sill so that the burner flow and oxidizing gas flow patterns are not such a problem to the hearth material and other furnace equipment mounted nearby. Further, the discharge opening of the particulate injector is also moved to the advantageous position.
Advantageously, the apparatus mounting aperture in the mounting enclosure is formed at an optimum angle, preferably 45 degrees for supersonic oxidizing gas flow, for the size and flow rate of the burner being mounted. The distance to the surface of the melt is reduced so that the supersonic oxidizing gas flow rate may be determined by the amount of oxygen needed in the steel making process at a particular point, rather than a larger flow rate needed to produce the required penetration of the melt from farther away. This causes the supersonic oxidizing gas to impinge on the slag and the melt in the furnace at an optimum angle and with an optimum flow rate.
The radiation from the arc increases according to the square of the distance as apparatus is moved closer to the center of the furnace. The mounting enclosure protects the apparatus from this harsh environment while it is located nearer the melt surface and center of the furnace while locating its discharge opening beyond the step to eliminate furnace structure considerations on the burner size and mounting particulars.
According to another aspect of the invention, locating the burner discharge opening nearer the center of the furnace by extending along the step with the mounting enclosure also has the advantage of producing a point of impingement for the oxidizing gas which is closer to the center of the furnace for the same angle and height above the surface. This means more of the oxidizing gas can react with the melt at earlier times in the melting and refining cycle and less reacts with the hearth and other related furnace parts on the outer edge of the process.